Modern automobile refinishing frequently involves partial repainting using factory-specification paints. Typically, an acrylic enamel or a two-part catalyzed urethane (enamel) paint is applied to a portion of the painted area of a vehicle. The ordinary masking or protecting procedure is to "paper mask" twelve to thirty-six inches of the area not to be painted. High quality shops will employ a plastic wrap or "bag" applied to the remaining area not to be painted because the paper mask does not always seal sufficiently well to prevent paint overspray from reaching the protected area, nor dirt and moisture from reaching the fresh paint. Overspray from these or other modern automotive paints sticks tenaciously (especially to glass and bright metal), and its removal is very tedious. Airborne dirt or moisture escaping from the bag can settle on the wet paint, causing a pebbly appearance or mottled finish which ca be thoroughly objectionable to the fastidious customer. Following repainting, the bag when used is ordinarily thrown away, resulting in extra shop waste. Despite these shortcomings, plastic bag masking is currently used, especially by quality shops.
Regardless of the procedure used, in the typical process the paper is cut away carefully around the area to be refinished and taped into place at the perimeter of that area. The plastic is also taped down.
From time to time, and especially in the early days of automobile refinishing, various water-washable liquid masking compositions have been proposed. Among these are the compositions of U.S. Pat. Nos. 1,795,455, 1,861,165, 3,846,172, 4,347,266 and 4,548,967 and PCT application No. W088/101156.
Although unrelated to paint masking, it should be noted that U.S. Pat. No. 4,315,779 discloses denture gel compositions containing glycerin (also known as glycerol), xanthan gum and other ingredients.